1. Technical Field
The invention relates to fiber optical couplers. More particularly, the invention relates to compact designs of polarization combiners/splitters including at least two collimators that are arranged in such a way that the overall size of the polarization couplers is reduced without loss of performance thereof.
2. Description of the Prior Art
Optical telecommunications generally involves the use of light beams propagating through optical fibers to transmit data from one end to another end. When an optical fiber carrying an input data signal that needs to be connected to two destinations, the signal needs to be split into two. This is achieved in the art by a coupler. When used for the splitting purpose, it is often referred to as a splitter. Generally, a coupler is bi-directional. When a coupler is used to combine two signals respectively from two sources, the coupler is used as a combiner to combine the two signals onto a single optical fiber.
As the light beams travel through the optical fiber, they may be distorted by the fiber in a number of ways. One type of distortion caused by optical fiber is polarization mode dispersion, which refers to an effect that an optical device may have on different polarizations of a light beam. In many applications, polarized light beams are used to ensure desirable effects of all optical devices involved. There is, therefore, a need for a polarization coupler that maintains respective polarization of light beams going therethrough while being small in size without compromising system performances thereof.
The present invention, generally speaking, provides compact design of optical couplers for combining two differently polarized light beams onto a collimator or splitting a composed light beam into two differently polarized light beams. The description herein is largely based on a polarization beam combiner (PBC) and is equally applied to a coupler used as a splitter. According to one embodiment, the polarization beam combiner employs a birefringent crystal to allow efficient combination of two orthogonally polarized light beams (e.g. pump lasers) into one composed or depolarized light beam. According to another embodiment, the size of the polarization beam combiner is minimized by using a pair of specially designed fiber collimators. As a result, a coupler, according to the present invention, uses less components, is of small in size and provides an easy-aligning structure. Further the coupler offers lower optical insertion loss with minimized physical size.
In one implementation, the present invention is an optical combiner for combining two differently polarized light beams onto a collimator. The combiner comprises two collimators outputting respectively a first and a second polarized light beams, wherein both of the two collimators have an outer diameter and a sleeve that is so shaped on one side that, when two such collimators are arranged next to each other, a distance between centers of the two collimators is less than the diameter; and a crystal receiving the first and the second polarized light beams respectively from the two collimators and combining the first and the second polarized light beams into a combined light beam.
In another implementation, the present invention is an optical splitter for splitting a composed light beam into two differently polarized light beams. The splitter comprises a crystal receiving an incoming light beam and splitting the incoming light beam into a first and a second polarized light beams; and two collimators coupled to the crystal at one end and respectively receiving the first and the second polarized light beams, wherein both of the two collimators have an outer diameter and a sleeve that is so shaped on one side that, when two such collimators are arranged next to each other, a distance between centers of the two collimators is less than the diameter.
One of the objects of the present invention is to provide an optical coupler that is small in size while providing an easy-aligning structure.
Other objects, features, and advantages of the present invention will become apparent upon examining the following detailed description of an embodiment thereof, taken in conjunction with the attached drawings.